Small files replaced w/o confirmation on Win SFTP servers

When WinSCP uploads any file less than about 100KB, and the destination Windows SFTP server has a same-named file, no confirmation box appears and the file on the server is auto-replaced.

When uploading to a Linux system running the built-in OpenSSH, the confirmation box appears as expected for all duplicate files, regardless of size.

The SFTP servers are these free Windows-based ones:
freeSSHd (<invalid hyperlink removed by admin>) and
Core FTP mini-sftp-server.

I've not tried it on a Win-based OpenSSH install.

Environment:

• Version of WinSCP: v4.0.3 and v3.8.2
  
• Protocol: SFTP-3 (when connected to either freeSSHd or CoreFTP servers)
  
• Interface style: Norton Commander and Explorer view
  
• Transfer mode: happens if set to either automatic or binary; didn't test for text
  

To reproduce the issue:

1. install CoreFTP mini-SFTP-server (simpler to set up) onto a Windows machine. I installed and tested on both XP and 2003 Server
   
2. launch and enter basic server setup info into CoreFTP--user, pw, port (22) and root path (I tested on My Documents\Downloads, as well as "D:\testFolder\") then click Start button
   
3. connect to SFTP server using WinSCP using same info as in CoreFTP setup. This can be from the same machine (connect to localhost), but obviously a remote WinSCP is preferred for a more real-world scenario
   
4. using WinSCP, upload a series of files from about 96KB to 102KB. Easiest way to find a range of incrementally larger files is at C:\WINDOWS\system32, sorted by size
   
5. re-upload the same files, either together or one at a time. The files less than 100KB will always be replaced without confirmation, while larger ones ask for confirmation
   

To confirm it's an issue with WinSCP and not the SFTP servers, optionally connect to SFTP using FileZilla and repeat steps 4 and 5 above.

Thanks for any help and/or insights.

I think it is server-side problem. But will check it nevertheless.

martin wrote:

I think it is server-side problem. But will check it nevertheless.

Hi, thanks for the quick response.

I thought it might be server-side too, but since it occurred against two different SFTP server applications, and the FileZilla SFTP client did not exhibit the same bug, it's an error condition that WinSCP probably ought to handle regardless.

I prefer WinSCP to FileZilla, and would hate having to switch over this. Most of the files I'd be transferring are small though (5-50KB).

Testing with Core FTP mini-sftp-server, I'm sure that it is a server-side problem. I do not know about a workaround that would not cause performance degradation, so I'm leaving this unsolved.